Reducing Settlement and Collapse of Gypseous Soil Using Geotextile Reinforcement

Collapsible soils are problematic soils that have substantial strength while dry but lose strength when wet, resulting in excessive settlements. Soil collapse occurs when increasing moisture weakens chemical or physical connections between soil particles, allowing the soil structure to collapse. The existence of these soils, often with significant gypsum concentration, created serious challenges for structures and major projects. The primary goal of this study is to conduct a series of model tests subjected to static vertical stress to assess the ability of soil stabilization using geosynthetics material by employing single, double, and triple geotextile layers put at various places. A unique model test configuration was employed for this testing. The gypseous soil used was brought from near Sawa Lake by coordinates (31◦18′42.83″N, 45◦00′49.36″E) in Al-Muthanna Governorate. The gypsum content was more than (37%). It was found that, the ultimate bearing capacity of dry and wet gypseous soil models had been determined by using Two Tangent Intersection technique. The results show the Settlement Reduction Factor (SRF) % and the ratio of decreasing the collapse magnitude (Δed )

Novel Approach to the Treatment of Gypseous Soil-Induced Ettringite Using Blends of Non-Calcium-Based Stabilizer, Ground Granulated Blast-Furnace Slag, and Metakaolin

Gypseous soil is one type of expansive soil that contains a sufficient amount of sulphate. Cement and lime are the most common methods of stabilizing expansive soil, but the problem is that lime-treated gypseous soil normally fails in terms of durability due to the formation of ettringite, a highly deleterious compound. Moisture ingress causes a significant swelling of ettringite crystals, thereby causing considerable damage to structures and pavements. This study investigated the suitability of various materials (nano–Mg oxide (M), metakaolin (MK), and ground granulated blast-furnace slag (GGBS)) for the stabilization of gypseous soil. The results showed soil samples treated with 20% M-MK, M-GGBS, and M-GGBS-MK to exhibit lower swelling rates (<0.01% change in volume) compared to those treated with 10% and 20% of lime after 90 days of curing. However, soil samples stabilized with 10% and 20% binder of [(M-MK), (M-GGBS), and (M-GGBS-MK)] exhibited higher strengths after 90 days of soaking (ranging from 0.96–12.8 MPa) compared to those stabilized with 10% and 20% lime. From the morphology studies, the SEM and EDX analysis evidenced no formation of ettringite in the samples stabilized with M-MK-, M-GGBS-, and M-GGBS-MK. These results demonstrate the suitability of M-MK, M-GGBS, and M-GGBS-MK as effective agents for the stabilization of gypseous soil.

Effect of Nano-Carbon on Geotechnics Features of Gypseous Soils

A Collapsing soil usually causes problems, this kind of soil has a substantial strength while it is dry, but it loses its strength while inundating and be subjected to extreme settlement. It is impossible to predict in advance the reactions of soils subjected to inundating (i.e. landslide otherwise an important soil settlement). The reduction in irreversible volumes of collapsing soil happens quickly as well as suddenly, once the reduction starts there will be no measurement to be executed which could halt such difficulty. As a result of the soak and leach that are resulting from the dissolute and clean out of gypsum, the collapsing potentials increase during the time. There are many studies in this field that indicated the possibility of modifying this soil by using nanomaterials. In this study, the nanomaterial used is nanocarbon and the soil is gypseous soil taken from Al-Najaf city in Iraq. This work studies the effect of adding nanomaterials on the gypseous soil and investigates its behavior before and after adding nanomaterial. The results showed that adding the nanocarbon affects the collapse potential which decreases by a percent meanwhile the soil cohesion decreased partly when the nanocarbon is added with 0.8% but the friction angle increased about 19%. The best proportion of using of the nanocarbon ranges between 0.8-1.2%.

Novel Approach for Suppression of Ettringite Formation in Sulfate-Bearing Soil Using Blends of Nano-Magnesium Oxide, Ground Granulated Blast-Furnace Slag and Rice Husk Ash

The treatment of sulfate-bearing soil with calcium-based stabilizers such as cement or lime often results in ettringite formation, consequently leading to swelling and strength deterioration. Ettringite formation has negative environmental and economic effects on various civil engineering structures. This study was conducted to investigate the use of different materials (nano–magnesium oxide (M), ground granulated blast-furnace slag (GGBS), and rice husk ash (RHA)) for gypseous soil stabilization to prevent ettringite formation. Various tests were performed, including flexural strength, unconfined compression strength, linear expansion, and microstructure analysis (SEM/EDX), on lime (L)-, (M)-, (M-RHA)-, (M-GGBS)-, and (M-GGBS-RHA)-stabilized gypseous soil samples to determine their properties. The results indicated that the swelling rates of the soil samples mixed with 20% M-RHA, M-GGBS, and M-GGBS-RHA binders were much lower (less than 0.01% of volume change) than those of the soil samples mixed with 10% and 20% lime-stabilized binders after a curing period of 90 days. Meanwhile, the strengths of the soil samples mixed with 20% of M-RHA, M-GGBS, and M-GGBS-RHA soil specimens after soaking of 90 days were obviously higher (with a range from 2.7–12.8 MPa) than those of the soil samples mixed with 20% of lime-stabilized binder. The SEM and EDX results showed no ettringite formation in the M-RHA-, M-GGBS-, and M-GGBS-RHA-stabilized soils. Overall, the test results proved the potential of M-RHA, M-GGBS, and M-GGBS-RHA as effective soil stabilizers.

Behavior of Square Footing Resting on Gypseous Soil and Surrounded by a Sheet Pile Wall

Laboratory model is used in this study to investigate the behavior of centrally loaded square footing resting on gypseous soil, and surrounded by a sheet pile wall at a distance of 2B from the footing edge and extend in depth to 2B as well. During this study the soil were subjected to ten cycles of saturation and drainage at one-week interval to simulate heavy rainfalls or floods. It should be noted that the soaking water were added only outside the area surrounded by the sheet pile. Four points were chosen to detect gypsum solubility, three of them below the footing edge at different depths and one outside the sheet pile wall for comparison. It has been found that the dissolved gypsum below the footing is significantly less than the one outside the sheet pile wall. For each cycle of saturation-drainage the gypsum content is found to be reduced by 3 % and 0.8 % for the outsider point and for average of the three points respectively. Settlement during first cycle of saturation – drainage was twice as the second cycle and about four times of the third cycle. However, this first cycle settlement is about 25 % of the settlement of footing where no sheet pile wall is used. To sum up, the sheet pile wall found to be an effective protection to reduce the collapsibility of gypsum soil and to reduce footing settlement.